Yellow Shore Crab

Scientific name:  Hemigrapsus oregonensis

Author: Noah Stewart

Photos: D. Young

Identifying features   The Yellow Shore Crab is characterized by its distinctive yellow to grey-green colouration though the the younger ones are commonly white with a mottled green pattern.  They also may appear rarely as a purple morph.   They can be as large as 49.5mm (1.9 inches) but are generally less than 42mm (1 inch).   They have a line of hairs (setae) on their legs which help distinguish them from their twin the Purple Shore Crab (Hemigrapsus nudus) which lacks hair.

Habitat  This is the most commonly seen crab in the Pacific Northwest.  It lives in intertidal zones under rocks but is also found around sandy shorelines and in mud flats, eelgrass beds and estuaries.  In mud flats it often uses the burrows made by mud shrimp. It is often found in the same place as the Purple Shore Crab (H. nudus) but has a preference for areas with lots of plant matter and slower currents.

Diet  They tend to not be picky when it comes to diet as they are more of the scavenger omnivore.  They will mostly feed on microorganisms such as algae and diatoms and will occasionally eat small invertebrates if they are able to.  They are also able to filter feed.

Reproduction  Its breeding season is usually concentrated in the earlier months of the year from around February to May and hatching will then occur in July. Also occasionally, there will be a second breeding season that would begin in August and with hatching occurring in September. It has the typical crustacean life cycle having the egg, zoea, megalops then adult stage like most crabs.

Fun Facts

  • It is capable of resisting hypoxic conditions unlike many other shore crabs
  • Feeds mainly at night
  • Occasionally has a parasitic isopod in its perivisceral cavity but can’t be seen by the naked eye


(2017, November 9). YouTube: Home. Retrieved January 26, 2024, from

Jensen, G. C. (2014). Crabs and Shrimps of the Pacific Coast: A Guide to Shallow-water Decapods from Southeastern Alaska to the Mexican Border. MolaMarine.

Rafter, M. (n.d.). Yellow Shore Crab (Marine Species of Crab Cove (Alameda, CA)) · iNaturalist. iNaturalist. Retrieved January 26, 2024, from

Sept, J. D. (2019). The New Beachcomber’s Guide to the Pacific Northwest. Harbour Publishing Company Limited.

Flat Porcelain Crab

Author: Leo Looi

Photos: Leo Looi & D. Young

Common Name: Flat Porcelain Crab 

Scientific name: Petrolisthes cinctipes

Size range: The carapace of the Flat Porcelain Crab is up to 2 cm (0.9in) across.

Identifying Features   The Flat Porcelain Crab looks stocky and has broad, flat, even-sized claws. Sometimes the claws are even 1.5-2 times larger than its body! Its main identifying features are light to dark brown carapace and the carpi of the claws do not have hair as well as the claw being a reddish-orange colour. Their carpus has a long anterior lobe extending over a quarter of the total carpus.


The Flat Porcelain Crab lives in abundance in the Pacific Coast tide pools and can be found under rocks in the upper and middle intertidal of shorelines near or on an exposed outer coast. They hide under stones and debris, between mussels, sponges, and mussel beds. They prefer rocky intertidal zones with plenty of organic matter and debris, often slightly muddy. They range from Porcher Island in Northern BC to Southern California. They generally have a noticeable gape in one of their claws, but the function of this is unknown as the pincers aren’t used in feeding.


The predators of the Flat Porcelain Crab include fish, racoons feeding along the intertidal zone and occasionally birds such as seagulls will eat them too. 


The Flat Porcelain Crab feeds on plankton, diatoms, and suspended detritus by using the feathery hairs on its maxillipeds, which it waves in the water. When feeding, the crab hides under stones, mussel beds, and sponges. When safely concealed, they eat by sweeping their feathery maxillipeds through the water like fine-meshed nets to capture diatoms and other drifting plants and animals.

Life Cycle

Male and female anomuran crabs press their ventral surfaces together and release eggs and spermatophores simultaneously. The female carries a ‘sponge’ of eggs brooded between the abdomen and the body. The fecundity varies with body size and sampling site from ~25 to 900 eggs over a range of carapace width of 3-10 mm. Each egg hatches into zoea, a larva armed with a long rostral spine, and two posterior spines, which drifts in the plankton. The zoea goes through a molt into a second zoea stage, then molts into a post-larval megalopa larva, with prominent eyes and fully developed appendages. The megalopa molts into a miniature ‘first crab’ which has features of an adult crab. 

This is the molt from the Flat Porcelain crab seen in the other photos.


Cowles, D. (n.d.). Petrolisthes eriomerus Stimpson, 1871. Retrieved January 15, 2024, from

iNaturalist Canada. (n.d.). Flat Crab (Petrolisthes eriomerus) · iNaturalist Canada. iNaturalist Canada. Retrieved January 15, 2024, from

Jensen, G. C. (2014). Crabs and Shrimps of the Pacific Coast: A Guide to Shallow-water Decapods from Southeastern Alaska to the Mexican Border. MolaMarine.

Matthews, C. (2020, June 15). Porcelain Crabs. Mayne Island Conservancy. Retrieved January 15, 2024, from

Petrolisthes cinctipes Flat porcelain crab. (2015, December 17). Mainpage Reeflex. Retrieved January 15, 2024, from

Squat Lobster

Author and Illustrator: Winifred Niedjalski

Photos: Thank you to Andy Murch for the use of his Photos.

Common Name: Squat Lobster

Scientific name: Munida quadrispina 

Length: Squat Lobsters range in size from one inch to four inches. Their carapace reaches up to 2.6 inches long, and their legs may be several times longer.


  • Legs: Squat Lobsters have ten legs, which vary in size. The first pair is small and primarily used to clean the gills. The second pair is the thickest and longest, containing claws for defence and cleaning. The remaining three pairs are slender and used solely for waking. 
  • Carapace: The carapace is lined with small spines and functions as a protective cover for the Squat Lobsters to protect the internal organs. The carapace has greater length than width and is a crucial aspect of structural support. 
  • Abdomen: The abdomen is located behind the carapace and tends to be more flexible, with no spines but a few ridges. Inside the abdomen, the Squat Lobster stores its tail. 
  • Tail: Squat Lobsters have a well developed tail located under a groove in their abdomen. The tail is fan-shaped and is used to swim backwards as a defensive mechanism. 
  • Coloration: The Squat Lobster is primarily a mix of red and orange. Its central portions of the body, the carapace and abdomen, are red-brown with a lighter ventral of red ridges and white grooves. More specifically, the Squat Lobster has blue spots along the cervical groove, which allows it to stand out among other lobster species. As for its legs, its chelipeds are red with white tips, and its walking legs have white bands progressing down the leg. Their tail is a light translucent orange. 

Habitat   The Squat Lobster is found worldwide, living in global oceans except for the cold Arctic and Antarctic waters. The species Munida quadraspina is located in Pacific Northwest waters from Alaska to California. In British Columbia, they are commonly observed at Cape Beale, Vancouver Island, but are known to be located up the coast.  

Generally, Squat Lobsters live in 12-1463 metres depts on graves, mud, and rocky faces. Throughout British Columbia, they populate the surfaces of deep-sea sponges, where there is a low current. 

Prey   Squat Lobsters are opportunistic feeders, meaning they consume various organisms depending on availability and habitat. They scavenge their location by excavating muddy or sandy deposits to sort for edible components with their mouths. In addition, they also prey on larger animals. Some of the organisms and animals they feed on include: 


  • Shrimp: Squat Lobsters consume benthic shrimp, disturbing both human shrimp traps and the shrimp ecosystem.
  • Detritus: A primary food source for the Squat Lobster is detritus, which is dead plant and animal matter.
  • Small Invertebrates: In addition to shrimp, Squat Lobsters have been observed preying on other small invertebrates, especially crustaceans local to the specific habitat.
  • Organic Particles: Squat Lobsters feed on organic particles found on the seafloor. Like detritus, organic particles contain dead plant and animal matter, but living organisms and other organic materials are also present.

Predators   The Squat Lobster is an essential aspect of the marine ecosystem, being prey for many organisms, including:

  • Fish: From juvenile to adult fish, many fish species are common predators of Squat Lobsters. In BC, fish such as cod, haddock, and striped bass pose a significant threat to the individual Squat Lobster.
  • Large Marine Mammals: Depending on the location, marine mammals such as whales, dolphins, sea lions, and sea otters feast on Squat Lobsters. In BC, sea otters, sea lions, and seals are marine mammals most likely to eat the population. 
  • Marine Birds: Seabirds may forage Squat Lobsters near the surface as part of their diet.
  • Crustaceans and Mollusks: Certain mollusks, such as Octopus and Squid, feed on Squat Lobsters, as well as crustaceans, such as Crabs.

Life Cycle   The life cycle of the Squat Lobster is similar to other crustaceans but contains some critical differences throughout the stages:

  • Eggs: It commences with the female laying eggs attached to her abdomen. 
  • Zoea Larvae: As the eggs hatch, the larvae are planktonic and drift freely in the water. The progression from this stage to the next is significantly shorter than other crustaceans, lasting only a few days. 
  • Megalopa Larvae: After multiple transformations, the larva transforms into megalopa larvae, the lost developed and defined stage.
  • Juvenile: The megalopa larvae metamorphose into a juvenile Squat Lobster, where it now becomes benthic, settling at the bottom of the ocean. 
  • Adult: In the final stage, the juvenile Squat Lobster grows into their distinct body shape and proceeds to live as an Adult Squat Lobster. 

As for timing, the Squat Lobster Munida quadrispina’s life cycle is poorly studied. However, a detailed study of M. subugosa, a species located in Argentinian waters, was observed to have a reproductive cycle starting in May and ending in September, just in time to line up with the autumn zooplankton blooms. If basing the cycle on the influence of blooms, it could be hypothesized that Munida quadrispina would follow the same schedule, starting with egg development in females during May and ending with larvae hatching in September. 

Fun Facts: 

Squat Lobsters currently contain 60 genera and over 900 species, with an estimated 120 species yet to be discovered.

To obtain food, Squat Lobsters sometimes steal food from sea anemones.

Unlike crustaceans who cannot swim and walk along the ocean floor, Squat Lobsters can swim actively. 

For defense, Squat Lobsters squeeze themselves between rocks, allowing them to defend with their large claws while keeping a defensive position.


Aquarium of the Pacific. (n.d.). Squat lobster. Retrieved January 22, 2024 from,pair%20has%20very%20small%20claws.   


BudSquat Lobster. (2023, September 11). Squat Lobster, Vancouver Island, British Columbia. Squat Lobster. Retrieved January 22, 2024 from  

Cowles, D. (2005). Munida quadrispina Benedict, 1902. Retrieved January 22, 2024 from  

Hart, J. (2021). Fauna BC: Electronic atlas of the wildlife of British Columbia. Retrieved January 22, 2024 from 

Purple Shore Crab

Scientific name:  Hemigrapsus nudus

Author: George Sleen

Photos: George Sleen and D. Young

Length: Male adult purple shore crabs typically grow to a width of 2.2 inches while females will grow to around 1.3 inches across

Identification:  The purple shore crab has a few distinct physical features:

  • Coloration: Like the name suggests, purple shore crabs are usually a dark red or purple in color, but there is also a green morph that has no spots on its claws.
  • Carapace: The carapace (the shell of the crab) is square in shape, and has a distinct hump on the back. It is widest at the level of the eyes and tapers towards the back.
  • Claws: The claws of the purple shore crab have distinct spots on their claws that help to differentiate them from the Yellow Shore Crab (Hemigrapsus oregonensis). They will also have a white tip on their legs and claws.

The green morph of the Purple Shore Crab

The purple shore crab shares many similarities with other shore crabs from the genus Hemigrapsus, especially the Yellow Shore Crab (Hemigrapsus oregonensis), which is why the spots on the crab’s claws are important to look at.  

Habitat:  The purple shore crab is found in the intertidal zone along the Pacific coast of North America. It inhabits rocky shores, tide pools, and sandy or muddy areas in the intertidal zone.  They are active during the day and hide during the night, often in crevices or under rocks. They can burrow in the sand or mud to stay moist during low tide.

Prey:  The purple shore crab is an opportunistic feeder, which means that it will consume a wide variety of organisms. They typically feed during low tide. Some of its known prey include:

  • Algae: Purple shore crabs consume various types of algae, including kelp and seaweed.
  • Barnacles: Purple shore crabs will feed on barnacles, both as adults and as juveniles.
  • Mollusks: Purple shore crabs are known to consume various types of mollusks, including mussels and snails.
  • Other crustaceans: Purple shore crabs can consume other crustaceans, such as small crabs and shrimp.
  • Organic debris: Purple shore crabs also consume detritus and other organic matter, such as dead fish and seaweed.

The diet of the Purple Shore crab may vary depending on the location and the availability of food.

The common purple form or the Purple Shore Crab beside the rarer green morph of the species.

It is quite common to find the molts of Purple Shore Crabs on the beach as in the photo above.  Though dead crabs may look similar, they are more likely the molts.  When the molts dry in the summer sun they turn a light red-orange colour.  You can really see the distinct red spots on the claws that are used to identify this species.

Predators:  The purple shore crab is an important prey item for many organisms and is known to have several natural predators, including:

  • Birds: Birds such as gulls, crows and other shorebirds feed on purple shore crabs, especially during the low tide when they are exposed.
  • Fish: Many types of fish will feed on purple shore crabs, as well as some other types of crustaceans.
  • Other crabs: Purple shore crabs are known to be preyed upon by other crabs, such as dungeness and red rock crabs.
  • Sea star: sea stars will feed on purple shore crabs, as well as other invertebrates if they get a chance.

Predation of the Purple Shore crab may vary depending on the location and the availability of other prey. Adult crabs have a better chance to survive from predation as they have a more developed carapace and better developed claws. Juvenile crabs are more vulnerable to predation.

Life Cycle: ​​  The Purple Shore Crab has a typical crustacean life cycle:

  • Eggs: Female Purple Shore Crabs carry the eggs in their abdominal flap, which are then fertilized by males and carried on the female’s abdomen.
  • Larvae: The eggs hatch into planktonic larvae, which go through several developmental stages, known as zoea, before going to the megalopa stage.
  • Juveniles: The megalopa stage settles on the bottom and begins to resemble an adult crab, but is still small and lacks adult characteristics.
  • Adults: The juvenile crabs continue to grow and molt, eventually reaching maturity and reproducing.

A female Purple Shore Crab carrying her eggs below her abdomen.


Brietzke, C., Fretwell, K., & Starzomski, B. (2016). Purple shore crab • Hemigrapsus nudus. Biodiversity of the Central Coast. Retrieved January 25, 2023, from

Cowles, D. (2005). Hemigrapsus nudus. Hemigrapsus nudus (Dana, 1851). Retrieved January 25, 2023, from

Gohiking. (n.d.). Purple Shore Crab, Vancouver Island, BC. Retrieved January 18, 2023, from

Seattle Aquarium. (n.d.). Purple shore crabs. Seattle Aquarium. Retrieved January 18, 2023, from

Common name: Western Sea Roach, Rock louse

Scientific name: Ligia occidentalis

Size: To 2.5cm (1″)

Author: Aina Saitoh

Photos: D. Young

The Western Sea Roach is an isopod within the subphylum Crustacea and phylum Arthropoda. Their bodies are flat and vary in colour including grey, yellow and brown. Their body is separated into seven main parts and their uropods (the long structures at their hind end) are quite long relative to the closely related species Ligia pallasi. They have special cells, chromatophores, which allow them to change their color to camouflage into the background.  They are generally lighter in colour during the night and then darken during the day time.  They live around the sea in part because they need to keep their gills, located near their posterior end, hydrated in order to breathe. However, they can drown if they are submerged so are considered to be largely a terrestrial organism.  They are very fast and will quickly hide in crevices along the rocky shoreline.  They are found above the water line up to the high tide line.  They are often active at night when they feed on microscopic algae (phytoplankton) and, as an omnivore, scavenge for a diversity of other food sources as well.

This rocky shoreline, located on a southern Gulf Island in British Columbia, is a typical habitat of the Western Sea Roach.  Many sea roaches, including the one in the photos above, were scurrying along these rocks on a warm summer day.


A Brief Encounter with a Western Sea Roach. (n.d.). Nature Chronicles. Retrieved January 23, 2023, from

Cowles, D. (n.d.). Ligia occidentalis. Retrieved January 23, 2023, from

General Format – Purdue OWL® – Purdue University. (n.d.). Purdue OWL. Retrieved January 23, 2023, from

Species Ligia occidentalis – Western Seaslater. (2010, May 5). BugGuide.Net. Retrieved January 23, 2023, from


Duane, S. J. (2019). The New Beachcomber’s Guide to the Pacific Northwest. Harbor Publishing.

Northern Kelp Crab

Common name: Northern Kelp Crab, Shield-Backed Kelp Crab

Scientific name: Pugettia producta 

Size range: Carapace 7.8-9.3 cm across, with differing appendage sizes 

Author: Ruby Wallace

Photography: Thank you to Andy Murch for permission to use his photos on our page!

Identifying Features:   Northern Kelp Crab are part of a superfamily of crabs called the Majoidea (spider crabs) and are most easily identified by their shield-shaped carapace and 4 long, hairless walking legs. Telling the difference between males and females is hard, but generally male Northern Kelp Crabs have a bigger carapace, averaging at about 9.3 cm across, and females about 7.8 cm across.  The second pair of their legs is the strongest and longest, being up to 1 ½ times their body length. Adult Northern Kelp Crabs are brown or red in colour, while juveniles are greenish-yellow. Unlike other crabs such as the Graceful Kelp Crab (Pugettia gracilis) who also have a shield-like carapace, the carapace of the Northern Kelp Crab is uniquely smooth and hard. The underside of the Northern Kelp Crab is usually red and/or yellow. You can sometimes tell when a Northern Kelp Crab hasn’t molted in awhile if their body is covered in the white and grey, mold-like appearance of invasive colonial tunicates. A Northern Kelp Crab after its terminal molt will often be covered in barnacles.

Habitat:  Northern Kelp Crabs live primarily along the West Coast of North America, from Southern Alaska to Northern Mexico. They occupy kelp beds and forests and are especially common in swaths of Bull Kelp. Juveniles have been spotted in tide pools or smaller beds of Rockweed or Surf grass. Adults can be found anywhere from intertidal zones, up to 73 meters down. At times, they are seen at wharf pilings. 

Food (Prey):   Generally, the Northern Kelp Crab is a nocturnal feeder. Most of the year, it is a herbivore and feeds on Kelps, seaweeds such as the red algae primarily in the spring and summer. One unique behaviour of the Northern Kelp Crab is that it does not camouflage on purpose like the Graceful Decorator Crab (Oregonia gracilis) or the Graceful Kelp Crab (Pugettia gracilis) does by covering their carapace in kelp. This is probably because the Northern Kelp Crab is faster and larger and has less need for strategic camouflage. The only time the Northern Kelp Crab is observed exhibiting this behaviour is to hold onto their food through the day – similar to a backpack – and only taking bites when needed, while freeing up the pincers for defense and communication. During the Winter months, when the kelp beds and algae have decreased in volume, Northern Kelp Crabs turn to a mainly animal-based diet of barnacles, bivalves, hydroids, and bryozoans. 

Predators:   Sea otters are the most common predator of the Northern Kelp Crab, as they are in heavy abundance in most kelp forests. Other predators include the Staghorn Sculpin, various gulls, and cabezons. Oftentimes the Zoea larvae of Northern Kelp Crabs are eaten by Velella velella. Parasites are also an issue for Northern Kelp Crabs, one such parasite; the Heterosaccus californicus causes the Northern Kelp Crab to become sluggish, and destroys the male reproductive organs. In turn, many males become hermaphroditic and develop female reproductive organs. One defense against predators that the Northern Kelp Crab possesses is its speed and relatively aggressive nature. Its pincers and hard carapace also offer some protection.  

Life Cycle:   Adult Northern Kelp Crabs migrate to deeper waters in the Fall to mate. Once the eggs of a female have been fertilized, they are stored in her abdombale sac, also called an pron. Females can be seen throughout the seasons carrying eggs. One clutch from a female can contain anywhere from 34,000 to 84,000 eggs. At first, the eggs are bright orange, then become red, and finally, before hatching, the eggs will become grey and purple. This process can take anywhere from 2 weeks to a month. After being hatched, the zoea larvae will drift away and develop into megalopae, and then into juveniles where they take on the green/yellow colouration. Embryonic development of Northern Kelp Crabs varies wildly but usually the entire process takes about 1 year. 

 Fun Facts: 

  • Like most Brachyura, the Northern Kelp Crabs cannot osmoregulate (cannot regulate internal balance of disolvants and fluid relative to surroundings) and therefore cannot survive in brackish water 
  • Though not considered a popular crab for commercial fishing, the taste of a Northern Kelp Crab has been described as “sweet” and the texture “stringy” 


Cowels, D. (2005) Pugettia producta (Randall, 1839). Invertebrates of the Salish Sea. Retrieved January, 29, 2022 from

NorCal. (Dec, 2005). Are Kelp Crabs Edible?. NorCal Kayak Anglers. Retrieved January, 29, 2022 from,any%20crab%20I’ve%20eaten. (2002). Kelp Crab Pugettia producta. Explore California Sanctuaries. Retrieved January, 29, 2022 from,about%2073%20meters%20in%20depth.

University of Puget Sound. (2022). Kelp Crab (Pugettia producta). Slater Museum of Natural History. Retrieved January 29, 2022 from

Taylor Coastal Shrimp

Author: Rubin Johnston

Scientific Name: Heptacarpus taylori

Size Range: The average length of adults is around 28mm (1.1 in)

Identifying Features: Taylor Coastal Shrimp have a variety of colours, including red, brown, black, and green. Two things that make this species stand out are the arched back, and the distinct white patches on the top of its head and body.  These patches may appear as separate patches or as a single large white patch similar to the one shown in the photos. 

This species is commonly found near the shore, often in tidepools.  They are omnivorous and will eat plants, plankton, and scavenge on dead animals.  They are near the bottom of the food chain, so they have many predators, like crabs, sea urchins, starfish, and seabirds.  Similar to other shrimp, during reproduction the male transfers a packet of sperm called a spermatophore to a pouch on the female’s abdomen.   The female will produce eggs that she keeps in the same pouch until hatching. When the eggs hatch, the larvae over multiple weeks drift along in the current as nauplius and then metamorphose into zoea.  The zoea larvae then develop into juvenile shrimp which can swim to food and usually end up by the shore, where they live and mate as adults.


Jensen, G. C. (2014). Genus Heptacarpus. In Crabs and shrimps of the Pacific Coast: A guide to shallow-water decapods from southeastern Alaska to the Mexican border (pp. 132–133). essay, MolaMarine.

Phronima Sedentaria

Scientific Name:  Phronima sedentaria

Author:  Eduarda Ferro Braga Laurindo Correia

Size Range:  These are tiny creatures with sizes ranging from 1.2-4.2 cm (~0.5 to 1.7 inches). 

Life Expectancy:  They live around one year. 

Identifying Features:  Phronima sedentaria can be distiguished by its very large head which is composed of two very large transparent compound eyes.  It also has two lateral compound eyes and 4 distinct red retinae.  The internal anatomy of these creatures is reasonably similar to that of other amphipods, but there are some key characteristics that differentiate them. As an example, their foregut is reduced and surrounded by a midgut chamber. Their brain is circumesophageal with four pairs of major nerves, that lead to their 4 compound eyes and to their ventral nerve cord and antennules. This organism has numerous specialized legs including two large claws, as well as a tail with 3 pairs of swimmerets (pleopods) it uses for swimming.  They also have pigmented-cells called chromatophores that are responsible for camouflage; these cells contract to give the organism a transparent appearance so it will be unseen or mistaken as harmless plankton by the prey. 

Mating Behaviour:  Males use their antennae to find potential mating partners in response to the release of pheromones by the females. The male will then ride or hold onto the female until she is ready to molt, the male will then push the sperm into the marsupium and release the female when it is complete. After a couple of hours, the female will release her eggs into the marsupium for fertilization.

Habitat:  They are usually found in temperate and tropical waters around the world and can live anywhere between the surface and deep water. 

Food:  Their feeding behaviours depend on the consistency of the food being eaten. The specialized legs called pereiopods are used during feeding to pick and pull prey with soft bodies toward their mouths, where the mouthparts are responsible for removing smaller pieces and directing them to the esophagus. When the tissue of the prey is tough other pereiopods work to keep it across the mouth cone area while the mandible breaks it down into smaller pieces. If the tissue is fluid-like, the contents will be sucked into the foregut with the help of the muscles of the esophagus and gut. One example of food they might ingest is zooplankton.

Predators:  Fish are some of the most prominent predators.

The photo above shows the adult female that ventured outside of the salp containing her juvenile offspring within.  

Life Cycle:  Phronima sedentaria make their homes in hallowed salps. They attack their victims by slicing them open with their claws, eating the soft tissue of the prey and then using the barrel-like leftovers as a gelatinous home. Females will lay their eggs in this barrel, which also provides protection from predators and space for food storage. These eggs will hatch inside of the barrel, and it will, later on, serve as food for the young amphipods. These young amphipods can be seen swimming around the barrel.  At times both the adult and juveniles in our lab could be seen leaving the barrel and re-entering it. 

Two juveniles inside the salp with their mother’s head above.

The visual system of Phronima sedentaria has been described as extraordinary and has often been studied.  The two median compound eyes are unusual in their size with crystalline cones reaching up to 5mm in length.  The structure is thought to give Phronima resolution under very low light levels while also  being transparent, a benefit when avoiding detection by predators.

The illustration on the right is adapted from Ball, E. E. 1977.  Fine structure of the compound eyes of the midwater amphipod Phronima in relation to behavior and habitat.  Tissue & Cell 1977 9 (3) 521-536

Video Production: Eduarda Ferro Braga Laurindo Correia

Photos and Video:  Misha Young and David Young

Special thanks for Misha for finding the specimen off the shores of Victoria.


Amphipod: Salp Invader. (2018, May 18). Retrieved January 25, 2021, from

Ball, E. E. (1977). Fine structure of the compound eyes of the midwater amphipod Phronima in relation to behavior and habitat. Tissue and Cell, 9(3), 521-536. doi:10.1016/0040-8166(77)90010-6

Diebel, Carol. (1988, January 1). Observations on the Anatomy and Behavior of Phronima Sedentaria (Forskal) (Amphipoda: Hyperiidea). Journal of Crustacean Biology, 8(1). Retrieved January 25, 2021, from

Phronima sedentaria. (n.d.). Retrieved January 25, 2021, from

Phronima sedentaria. (n.d.). Retrieved January 25, 2021, from

Van Couwelaar, M. (n.d.). Zooplankton and Micronekton of the North Sea. Retrieved January 25, 2021, from

Young, L. (n.d.). A Plankton Species Straight Out Of A Horror Movie. Retrieved January 25, 2021, from

Gammarid Amphipod

Common Names: Amphipod

Author and Photographer:  Samantha O’Keefe

February 19, 2013 Plankton Tow – Cadboro Bay

Umbrella Crab

Authors: Fai &Vivian

Scientific name:   Cryptolithodes sitchensis

Common name: Umbrella crab, Sitka crab or Turtle Crab    

Size Range:  5 – 10 cm (2.0 – 3.9in)

Identifying Features

The Umbrella Crab is a species of Lithodid crustacean native to coastal regions of the northeastern Pacific Ocean, ranging from Sitka, Alaska to Point Loma, California. They have a half-moon shaped carapace extending over all of their eight walking legs and two chelipeds. The carapace can be 5–10 cm (2.0–3.9 in) at the adult stage and has scalloped edges. This carapace ranges from neutral sandy colors to bright oranges, reds, and purples.



Umbrella Crabs can be found on bedrock. They live within 18 m (59 ft.) of the intertidal zone along the exposed coasts of the Pacific Ocean. Intertidal species of Lithodidae prefer habitats of cooler temperatures ranging from 0–25 °C (32–77 °F).



Umbrella Crabs feed mostly on algae and tiny sessile organisms.



The major predators are otters, sea birds, octopuses and other marine animals. They have a few defenses to avoid being eaten. Their shell is their first layer of defense. While their shell may not deter the aforementioned predators, they do ward off animals that cannot crush or open them. When threatened. The best defense is the anemone: it catches bits of food off of the crab’s shell and, in return, it defends the crab from predators by stinging animals with it’s poisonous tentacles.


Life cycle

The Umbrella Crab reproduces sexually, using the molting cycle. There are six stages in the development of this crab similar to other crabs: Eggs, Prezoea, Zoea, Megalops, Juvenile Instar and Adult Crab.



Its distinctive shell allows it to camouflage itself into its surroundings. It is often mistaken for an old clam shell or patch or coralline algae.

Photographs by D. Young


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